In general, foods, medicines, cosmetics and other substances packaged in containers are oxidized by ambient air, resulting in degradation of the quality of the substance. In the prior art it is well known to remove oxygen from the headspace of a container by replacing the ambient air in the headspace with inert gas during filling of the containers.
In particular, oxidative degradation is one of the major causes of the spoilage of sterilized packaged food product. This degradation is the result of direct contact of oxygen with the food product and reaction therebetween during extended storage of the packaged food product. The spoilage is increased at higher storage temperatures. Certain non-food products must also be protected from oxygen.
While expensive packaging can be designed to keep oxygen away from the food product, certain products must be packaged with a headspace volume for mixing and pouring. When the headspace is filled with ambient air, the headspace volume contains 21% oxygen which should be removed.
A prior art apparatus for reducing the amount of oxygen in the headspace of a gable-top container is disclosed in U.S. Pat. No. 4,869,047 to Nishiguchi et al. In accordance with this teaching, a gas substitution station with a pair of inert gas-filling nozzles is arranged between the filling and top sealing stations. The first nozzle has a greater area than the second nozzle. Inert gas injected into the headspace by the first nozzle displaces the ambient air. The second nozzle is arranged to inject more inert gas into the headspace as the top fins of the carton are being brought toward each other preparatory to the top sealing step.
The arrangement of Nishiguchi et al. suffers from the disadvantage that because the outlet of the nozzle is circular and the cross section of the carton is square, the ambient air in the corners of the carton is not easily displaced. Moreover, for the foregoing reason and further because the injected inert gas initially flows radially outward and then upward along the inner wall of the carton, turbulent flow can result which serves to trap ambient air in the headspace.
Another arrangement for reducing the amount of oxygen in the headspace of a container is disclosed in U.S. Pat. No. 4,870,801 to Mizandjian et al. In accordance with this teaching, deoxygenation of each container is performed under inert atmosphere by means of two simultaneous injections of inert gas. The inerting device comprises an insulating cap for preventing the entry of oxygen into the packages, an inert gas feed circuit for filling the cap with inert gas and a purging gas feed circuit for flushing the packages with inert gas.
Although Mizandjian asserts that their method results in a reduction of the oxygen content to below 2%, the arrangement disclosed is disadvantageous because it requires a complex injector design.
Using conventional packaging machines running at standard form/fill/seal rates, it has been possible to reduce the amount of oxygen in the headspace from 21% to 3-6% by volume. Such conventional packaging machines employ equipment for flushing the headspace with an inert gas such as nitrogen, which is substituted for the ambient air in the carton headspace.
However, oxygen levels of 3-6% by volume in the headspace are too high to provide optimum protection against degradation for those food products requiring a shelf-life of at least one year at room temperature and under dry-shelf storage conditions. Instead a headspace oxygen level averaging less than 1% by volume is required.